Influence of Hydrogen-Containing Fuels and Environmentally Friendly Lubricating Coolant on Nitrogen Steels’ Wear Resistance for Spark Ignition Engine Pistons and Rings Kit Gasket Set

In this study, modern nitrogen steels used for the manufacture of rings for Honda engines (70CC, 90CC, CRF70F, XL70, XR70, C70, CT70, ATC70, CL70) as well as other transport tribotechnical units was investigated. Due to the present ecological situation in the world, new environmentally friendly lubricating fluids for nitrogen steels’ tribotechnical units and surface treatments have been proposed. The results of tribotechnical tests are presented in the form of diagrams, graphs and step polynomials obtained by mathematically describing the changes in wear intensity when the load changes for different lubricating fluids. Friction pairs were compared with ShellHF-E 46 (synthetic lubricating fluid), ShellHF-R (biological origin) and lubricating and cooling liquids with 1%, 3% and 5% vegetable oil concentrations. In tribocoupling it was found that hydrogen diffuses into the metal because the tribodestruction of lubricating coolants plays an active role in the destruction of friction surfaces.

SPECIFIC FEATURES OF STRUCTURAL-PHASE TRANSFORMATIONS AND HARDENING DURING SHEAR DEFORMATION UNDER PRESSURE OF HIGH-NITROGEN STEEL WITH AUSTENITIC-FERRITIC STRUCTURE OF METAL MATRIX

The increased anticorrosive, strength, tribological, and physical characteristics are the specific features of steels with high nitrogen content. Searching for the ways to strengthen high-nitrogen steels is a promising area of contemporary metal science. Heat treatment is one of the methods of hardening nitrogen steels as a result of precipitation hardening with nitride particles. The authors studied the influence of short-term high-temperature aging and large plastic deformations implemented by shear under the pressure of 8 GPa (SP method) on Bridgman anvils (three revolutions of anvils with the rotation velocity of 0.3 rev/min) at room temperature on the structural-phase transformations and micromechanical properties of the 08H22GA1.24 high-nitrogen steel with the mixed γ (austenite) +  (ferrite) metal matrix structure. The study identified that aging (0.5 h) at the temperature of 650 °С of steel quenched at the temperature from 1180 °С causes the formation of the mixed austenitic-ferritic structure of metal matrix in the ratio of 50 vol. % of  and 50 vol. % of α and the release of extended secondary Cr2N chromium nitrides, together with ferrite interlayers forming the areas with the pearlite-like structure. These areas cause the increased microhardness of steel with the austenitic-ferritic matrix structure (385±8 HV 0.025) compared to one of steel aged at the temperature of 550 °С (0.5 h) and having an austenitic matrix structure strengthened with secondary CrN nitrides (364±8 HV 0.025). The SP deformation of steel aged at the temperature of 650 °С (0.5 h) with the initial ++Cr2N structure leads to →ʹ transformation and the formation of submicro- and nanocrystalline structures. It causes the effective strength improvement of steel (up to 900±29 HV 0.025) and the growth of resistance to elastoplastic deformation compared to aged at the temperature of 550 °C (0.5 h) condition.

High nitrogen steels

The article provides a brief overview of the properties and production technology of high-nitrogen steels (HNS), which have several advantages over traditional ones. The main advantages are: up to four times higher yield strength with unique preservation of the remaining characteristics; reduction in consumption or a 100 % elimination of the use of some expensive alloying elements, such as Ni, Mo, Co, W, and others; effective alloying with unconventional elements (Ca, Zn, Pb, etc.). The basics of HNS technology, dependence of the properties on nitrogen content in steels, producing technologies for ferritic-pearlitic, martensitic and austenitic steel, their properties and applicability are discussed. Alloying with nitrogen for ferritic-pearlitic steel requires more precise adherence to the chemical composition in order to prevent the formation of insoluble nitrides during heat treatment (due to its greater solubility compared to carbon). Features of martensitic steels are associated with the possibility of formation of nitrides and carbonitrides during tempering. The possible effect of nitrogen in these steels may be as a decrease in the size of nitride particles as compared with carbide ones. Increased stability temperature of nitrides and carbonitrides provides increased mechanical and physical properties. In austenitic steels, nitrogen, due to the strong γ-forming equivalence to nickel, replaces it in a ratio of 1 kg of nitrogen ≈ 6 – 39 kg Ni. In austenitic-martensitic steels, the main role is played by thermal martensite. Stable austenite is obtained in the process of its aging at operating temperatures. Examples of effective use of HNS in important details are described.

Wear resistance of hydrogenated high nitrogen steel at dry and solid state lubricants assistant friction

Purpose: This paper is devoted the investigation hydrogen influence on of wear resistance of high nitrogen steel (HNS) at dry and solid state lubricants assistant friction. It has been established that after hydrogenation at 250 N loading the wear rate increased by 2.9 ... 4.1 times. Microhardness of hydrogenated layer was 7.6 ... 8.2 GPa, that is increased after hydrogenation in two times. After adding the (GaSe)xIn1-x compounds to the tribo conjugates by X-ray diffraction analysis it has been established the appearance of new phases which formed during the friction process and detected on the friction surface. Design/methodology/approach: This work presents research results concerning the comparative tests of high nitrogen steels in the circumstances of dry rolling friction. It was conducted the experiments to determine the tribological properties of high-nitrogen steels under rolling friction. The test pieces were manufactured in the form of rollers, and rotated with a linear velocity 2.27 m/s (upper roller), 3.08 m/s (bottom roller). Upper roller is made from HNS was subjected for hydrogenation. Analysis of friction surfaces indicates the complex mechanism of fracture surfaces. The results of the local X-ray analysis and X-ray diffraction analysis has been established the appearance of new phases and elements on the friction surface. Findings: It has been found that the level of wear resistance of the investigated materials under hydrogenation. Compounds realize chemisorption, tribochemical mechanisms of the formation of thin protective (anti-wear, antifriction) layers on metal surfaces. Research limitations/implications: An essential problem is the verification of the results obtained using the standard mechanical tests, computer-based image analysis and other methods. Practical implications: The observed phenomena can be regarded as the basic explanation of reduces the plasticity characteristics after hydrogenation. Applying the (GaSe)xIn1-x compounds as a lubricant will allow the formation of films on friction surfaces that can minimize surface wear, which will contribute to the transition to a wear-free friction mode. The protective film is a barrier to high shear and normal loads, preserving the base metal of the part and providing reduced wear and friction. Originality/value: The value of this work is that conducted experiments permit to determine the tribological properties of high nitrogen steels under rolling friction after hydrogenation. After adding (GaSe)xIn1-x compounds to the tribo conjugates after due to X-ray diffraction analysis it has been established the appearance of new phases which formed during the friction process and detected on the friction surface.

NITROGEN STEELS AND HIGH NITROGEN STEELS. INDUSTRIAL TECHNOLOGIES AND PROPERTIES

Nitrogen pressure can be a basis for the most general classification of steel, alloyed by nitrogen. Nitrogen steels are made under normal pressure, high nitrogen steels are made under pressure that is higher than atmospheric in special units. Nitrogen, as well as carbon, also strengthens austenite, but increases thermal stability of austenite, has the smaller sizes of ions and high solubility in γ- and α-phases. The result is smaller size of nitrides, smaller superficial energy, their higher strengthening effect and possibility of simultaneous increase in durability and corrosion resistance of austenite. The article considers the mechanisms of nitrogen influence on properties of steel, thermodynamics and kinetics of steels alloying with nitrogen, critical concentration of nitrogen and influence of nitrogen on properties of steel. There is no uniform balanced database and thermodynamic model now. Therefore any choice of values of equilibrium constant and parameters of interaction according to tabular data reduces the accuracy of calculations of nitrogen solubility in steel. In the circumstances it is better to use experimental data for concrete alloy from original works. At the choice of data it is necessary to be guided by the following control values: KN = 0,044, A ≥ 600. The nitrogen solubility in liquid metal, in α- and γ-phases is significantly various. Critical nitrogen concentration Nk, which excess leads to formation of bubbles and interstices at steel solidification, depends on composition of steel. Now the acceptable results when determining critical nitrogen concentration, can be received from the following condition: during the whole time of solidification the nitrogen content in residual liquid has to be less its equilibrium with the general pressure in the system of content in liquid metal at the same temperature T. Examples of nitrogen and high nitrogen steels, including steels with special properties, such as corrosion-resistant in bioactive environments, bactericidal steel, alloyed according on the scheme C + N steels, are given.